1. Field of the Invention
The present invention relates to a chain wherein a lubricating oil is held between a pin and a bush which connects a pair of inner link plates, and is rotatably disposed on the outer periphery of the pin which connects a pair of outer link plates.
2. Description of the Prior Art
A chain is formed by continuously connecting a pair of outer link plates with a pair of inner link plates. A bush which connects the pair of inner link plates is rotatably positioned on the outer periphery of a pin which connects the pair of outer link plates so that the pin and bush may rotate relatively with each other. Thus, if the chain runs circularly between both driving and driven sprockets, the pin and bush frictionally slide with each other. There is already known a chain wherein a slight clearance between the pin and bush is filled with lubricating oil such as a grease, so as to lubricate the frictionally engaging surfaces and prevent wear. In this kind of chain, a sealing member is required to seal and hold the lubricating oil, and a ring-shaped sealing member is provided on the outer periphery of the pin between the outer and inner link plates.
A conventional sealing ring has a circular cross-sectional shape and is in elastic contact with both outer and inner link plates on both sides and with the outer peripheral surface of the pin on the inside surface. The sealing function of such sealing ring is insufficient and the sealability for the lubricating oil is questionable, because when applying the sealing ring on the outer peripheral surface of the pin, the lubricating oil already held between the pin and bush is compressed and the reaction thereof acts on and expands the ring radially outwardly. As a result, the sealing ring is expanded and deformed, permitting the lubricating oil to leak out through the inner peripheral surface of the sealing ring. Due to the imperfect sealability of the sealing ring, not only is the smooth rotation of the pin and bush questionable but also the chain is susceptible to early wear to elongation thereof, and to reduced life and durability.
There has also been considered a sealing ring of X-shaped cross-section instead of circular shaped cross-section, in order to attain a favorable sealability. However, because the applied position of the sealing ring is between the outer and inner link plates and the bush is slidable in the axial direction of the pin, it is clear that the sealing ring functions not only as a sealing member for the lubricating oil but also as a spacer for both link plates. In other words, the axial load is applied to the sealing ring due to the axial slide of the bush. Therefore, if the sealing ring is formed to be X-shaped in cross-section, it is too soft to bear the load and is not adapted for use as a spacer member.
Other problems still remain in conventional sealing rings. Even if the clearance between the pin and bush is filled with a lubricating oil as described above, the amount to be filled in the clearance is so minor that the prevention of wear of the pin and bush over a long period of time is not guaranteed. Further, the temperature of the lubricating oil rises naturally due to sliding friction between the pin and bush. It is noted that when the chain engages with the sprocket, the relative rotation of the pin and bush causes the lubricating oil to move slightly in the peripheral direction, but the relative rotational angle of the pin and bush is so small that the lubricating oil will not circulate around the pin and the oil will not be cooled.
A further important problem in this connection, is that heat is generated at a part to which a load is applied and at which the pin and bush substantially contact each other. When the chain runs with the rotation of the sprocket, a tensile force acts on each link plate and the tensile force on the inner link plate is transmitted to the bush. Therefore, the pin and bush contact each other in a part of the bush in the vicinity of which the inner plate is connected, but do not contact uniformly over the entire length of the bush, and thus contact is made locally. The contacting part is a load point. At this load point, the pin and bush directly contact each other without an intermediate oil film and therefore heat is generated locally on the bush. This heat will deteriorate the lubricating oil and will reduce the functioning of the oil. If the amount of lubricating oil to be charged is minor as described above, the influence of this heat deterioration becomes large. Particularly, even if the pin and bush rotate relatively, if the lubricating oil does not substantially flow and circulate as described above, no fresh lubricating oil will be fed to the heat generating part, i.e., the load point, the heat generating temperature will rise further and wearing at the load point will be accelerated.
The present invention provides a solution to the conventional problems described above.